(a) Field of the Invention
The present invention relates to a thin film transistor, an organic light emitting display (OLED) device including the thin film transistor, and a manufacturing method of the same.
(b) Description of the Related Art
An active matrix flat panel display generally includes a plurality of pixels arranged in a matrix and displays images by controlling the luminance of the pixels based on luminance information indicative of a desired image. One type of active matrix flat panel display is an organic light emitting display (OLED).
An OLED is self-emissive. OLEDs have desirable characteristics such as a relatively wide viewing angle, a relatively fast response time, and a relatively high contrast ratio when compared to liquid crystal displays (LCDs). Further, because an OLED does not require a backlight assembly, OLEDs are lighter and consume less power than LCDs.
A pixel of an OLED includes a light emitting element, a driving transistor, and a switching transistor. The transistors can be a thin film transistor (TFT). The active layer of the TFT can be formed of polysilicon or amorphous silicon.
While the deposition temperature of the amorphous silicon is low and it is convenient for manufacturing TFTs, the electron mobility thereof is low and the amorphous silicon TFT doesn't provide a sufficient driving current. Also the threshold voltage of the amorphous silicon TFT easily shifts over time.
While the electron mobility of the polysilicon TFT is high, off current thereof is high such that crosstalk may occur.
In the case of the polysilicon TFT, the polysilicon is generally formed on a substrate, and an ohmic contact layer, a gate insulating layer, and a gate electrode are formed sequentially.